I have gotten a request to write on personality types. This happens to be a topic I quite enjoy. In fact I have a three inch thick book that I stashed on my personal bookshelf (it used to live on my parent's) and I read it somewhat regularly.
Okay, you're asking, what does personality typing have to do with writing books? Plenty. I have found personality typing to be invaluable when it comes to keeping my characters in-character. You see, believe it or not, most people match up to what their personality type says they should be like. Therefore, if something holds true for people, how should it not also hold true for characters as well?
There are two types of personality typing that I use. One is the DISC method and the other is the Myers Briggs method. The first has only four main personalities, whereas the other has sixteen. The DISC method is much older, under the old names for the four personalities: Choleric is now D, Sanguine is now I, Phlegmatic is now S, and Melancholy is now C. Myers Briggs personalities are combinations of letters: E or I for Extrovert or Introvert, S or N for Sensing (Concrete thinkers) or iNtuitive (Abstract thinkers), F or T for Feeling or Thinking, and J or P for Judging (Schedulers) or Perceiving (go-with-the-flowers)
I highly suggest you get a book about them. The book I have on my shelf is Please Understand Me II: Temperament, Character, Intelligence. It uses the Myers Briggs method. It tries to convince us that Myers Briggs is merely an expansion of the other, but on that I disagree. You see, I had typed myself to be an I in the DISC method, and in the Myers Briggs, I typed myself to be an ENFP. However, according to this book, ENFP falls under the D category. Therefore, I use DISC for the most part separate from Myers Briggs.
When I develop characters, I almost always try to type them as quickly as possible. For instance, I found it great help in writing Sew, It's a Quest to know that Robin was an I-ENFP (like me ... although She is actually borderline ESFP. [and she's much better than me with a sword]), that Robert was a C-INTJ (like my mom. She was great help with deciding what he would be most likely to do in any given situation) Rosamond was a S-INFJ ... and so on.
Now, you don't have to make your character cookie cutter to the description of the personality type you decide the character to be. In fact, don't make him cookie cutter. No live person is cookie cutter, so why should your character be? For instance, Robin is quite a bit more of a hothead than most I's or ENFP's, however, she's still an I-ENFP, just a hotheaded I-ENFP.
So, get yourself a good book on personality typing - it doesn't have to be the one I use, it just has to be a good one. Read it, get to know it. You'll find that your characters have much more depth after doing so.
Now, that's all I have to say on this topic. Leave a review if you have a request, and I might just write it!